The present invention relates generally to the construction of walls and shells, and particularly to the construction of reinforced concrete walls such as those used in liquid storage tanks.
Substances such as liquefied natural gas (LNG), ethylene, propane, and butane are often stored in full-containment, low-temperature or cryogenic storage tanks. Such tanks often include a reinforced concrete wall and a thin metal vapor barrier. In some cases, the vapor barrier is secured to the interior surface of a reinforced concrete wall.
At least one such storage tank was built in the United States using precast concrete panels to form double walls. The panels were erected in two rings, and then apparently supported circumferentially by wrapping post-tensioning cable around the exterior of each ring. The post-tensioning cable was then covered with sprayed concrete. The outside wall was completed by pouring concrete against the interior surface of the outside ring. In other contexts, steel liners have been used on concrete panels.
Conventionally, however, the walls for storage tanks are built by pouring the entire, full thickness of the wall. For a conventional 35-meter tall storage tank having a 160,000 cubic meter capacity, it may take a year or more to gather the materials for and build the wall for such a tank.
The time required for building the wall can be important. In many projects, the roof of a storage tank is assembled at ground level within the interior of the wall. Once assembled, the roof is raised by air pressure and secured in place above the wall. After it is has been raised and secured, the roof provides a protected interior environment that is often important for finishing the interior of the tank.
Providing a quicker way to provide a protected interior environment could allow the interior work to begin sooner. Because the interior work is often on the critical path of projects involving the construction of liquid storage tanks, speeding up the time when such work can begin can sometimes result in a significantly shortened schedule for such a project. In projects involving the construction of a re-gasification terminal, shortening the construction schedule by two months could reduce construction costs and increase value to the owner by approximately $10 million.
In addition to the general advantages of reduced schedule, reducing the time required to construct the wall provides a unique advantage in regions such as Alaska that have hostile climates and a limited construction season. If the wall can be built and the roof secured above the wall during a summer construction season, work can continue in the interior environment through the winter.